Cartilage-inducing factor-B is a unique protein structurally and functionally related to transforming growth factor-beta

Periodontal regeneration: potential role of bone morphogenetic proteins

Initiation of osteogenesis and cementogenesis is a problem central to periodontal regeneration. A major advance in the understanding of bone formation has been the identification of an entirely new family of protein initiators, the bone morphogenetic proteins, that regulate cartilage and bone differentiation in vivo. The purification, genetic cloning and expression of recombinant human bone morphogenetic proteins (BMPs) have laid the foundation for the cellular and molecular dissection of bone development and regeneration. The striking evolutionary conservation of the BMP genes indicates that they are critical in the normal development and function of animals. In addition to postfetal osteogenesis, the BMPs may play multiple roles in embryonic development and organogenesis, including skeletogenesis and the development of craniofacial and dental tissues. The availability of recombinant human BMPs provides several challenges and opportunities to gain insights into the mechanisms regulating the regeneration of bone and cementum for optimal outcome in the periodontal patient.

Opposite effects of osteogenic protein and transforming growth factor beta on chondrogenesis in cultured long bone rudiments

Osteogenic protein-1 (OP-1, also called BMP-7) is a bone morphogenetic member of the TGF-beta superfamily. In the present study, we examined the effect of recombinant human OP-1 on cartilage and bone formation in organ cultures of metatarsal long bones of mouse embryos and compared the OP-1 effects with those of human TGF-beta 1 and porcine TGF-beta 1 and beta 2. Cartilage formation was determined by measurement of longitudinal growth of whole bone rudiments during culture and by the incorporation of 35SO4 into glycosaminoglycans. Mineralization was monitored by 45Ca incorporation in the acid-soluble fraction and by measuring the length of the calcifying center of the rudiment. Toluidine blue-stained histologic sections were used for quantitative histomorphometric analysis. We found that OP-1 stimulated cartilage growth as determined by sulfate incorporation and that it increased remarkably the width of the long bones ends compared with controls. This effect was partly caused by differentiation of perichondrial cells into chondrocytes, resulting in increased appositional growth. In contrast to OP-1, TGF-beta 1 and beta 2 inhibited cartilage growth and reduced the length of whole bone rudiments compared with controls. In the ossifying center of the bone rudiments, both OP-1 and TGF-beta inhibited cartilage hypertrophy, growth of the bone collar, and matrix mineralization. These data demonstrate that OP-1 and TGF-beta exhibit opposite effects on cartilage growth but similar effects on osteogenesis in embryonic mouse long bone cultures. Since both OP-1 and TGF-beta have been demonstrated in embryonic cartilage and bone, these results suggest that they act as autocrine or paracrine regulators of embryonic bone development.

beta ig-h3: a transforming growth factor-beta-responsive gene encoding a secreted protein that inhibits cell attachment in vitro and suppresses the growth of CHO cells in nude mice

beta ig-h3 is a novel gene first discovered by differential screening of a cDNA library made from A549 human lung adenocarcinoma cells treated with transforming growth factor-beta 1 (TGF-beta 1). It encodes a 683-amino-acid protein containing a secretory signal sequence and four homologous internal domains. Here we show that treatment of several types of cells, including human melanoma cells, human mammary epithelial cells, human keratinocytes, and human fibroblasts, with TGF-beta resulted in a significant increase in beta ig-h3 RNA. A portion of the beta ig-h3 coding sequence was expressed in bacteria, and antisera against the bacterially produced protein was raised in rabbits. This antisera was used to demonstrate that several cell lines secreted a 68-kD beta IG-H3 protein after treatment with TGF-beta. Transfection of beta IG-H3 expression plasmids into Chinese hamster ovary (CHO) cells led to a marked decrease in the ability of these cells to form tumors in nude mice. The beta IG-H3 protein was purified from media conditioned by recombinant CHO cells, characterized by immunoblotting and protein sequencing and shown to function in an anti-adhesion assay in that it inhibited the attachment of A549, HeLa, and WI-38 cells to plastic in serum-free media. Sequencing of cDNA clones encoding murine beta ig-H3 indicated 90.6% conservation at the amino acid level between the murine and human proteins. Finally, the beta ig-h3 gene was localized to human chromosome 5q31, a region frequently deleted in preleukemic myelodysplasia and leukemia. The corresponding mouse beta ig-h3 gene was mapped to mouse chromosome 13 region B to C1, which confirms a region of conservation on human chromosome 5 and mouse chromosome 13. We suggest that this protein be named p68 beta ig-h3.

Transforming growth factor-beta and bone morphogenetic protein-2 act by distinct mechanisms to promote chick limb cartilage differentiation in vitro

A number of studies suggest that several members of the transforming growth factor-beta (TGF-beta) family of peptide growth factors may be involved in the regulation of cartilage differentiation. It has been previously reported that TGF-beta 1 and TGF-beta 2 promote the chondrogenic differentiation of chick limb mesenchymal cells in high density micromass cultures (Kulyk et al. [1989a] Dev. Biol. 135:424-430). In this study we report that chick limb mesenchymal cells express mRNA for chicken TGF-beta 1, TGF-beta 2, and TGF-beta 3 during cartilage differentiation in vitro. In addition, the time course of their expression during cartilage differentiation is consistent with their playing a role in the initiation of this differentiation process. We also report that two members of the TGF-beta family, TGF-beta 3 and bone morphogenetic protein-2 (BMP-2), are capable of promoting the accumulation of cartilage extracellular matrix molecules by differentiating chick limb mesenchymal cells in micromass culture. Significant differences, however, were noted between the specific effects on matrix production elicited by these two growth factors which suggest that they may be acting by distinct mechanisms to regulate cartilage matrix production. TGF-beta appears to be most effective on cells which have not yet undergone cell condensation, a critical event in early cartilage differentiation, whereas BMP-2 is most effective after cells have condensed or differentiated. These observations suggest that TGF-beta 3 and BMP-2 may be acting in a sequential manner to regulate chick limb mesenchymal cells through the different stages of cartilage differentiation.

Effects of transforming growth factor beta and interleukin-1 beta on [3H]thymidine incorporation by human articular chondrocytes in vitro

This is a study of the regulation of human articular chondrocyte proliferation by transforming growth factor beta (TGF beta) and interleukin-1 beta (IL-1 beta) in vitro. Human articular chondrocytes were cultured at different cell densities on plastic and on a collagen substratum, in the presence and absence of serum. The effects of TGF beta and IL-1 beta on proliferation of chondrocytes, as determined by [3H]thymidine incorporation, under these conditions of culture were examined. TGF beta was found to have both stimulatory and inhibitory effects on chondrocytes in vitro. Interactions between TGF beta and growth factors present in serum influence the modulation of chondrocyte proliferation by TGF beta. IL-1 beta caused a significant reduction of the TGF beta-stimulated increase in chondrocyte proliferation. The complex inter-relationships between TGF beta and IL-1 beta on chondrocytes have implications for cartilage repair.

Effect of local injection of activin A on bone formation in newborn rats

In order to examine the effect of activin A on the process of bone formation, activin A was injected onto the periosteum of parietal bone in newborn rats, and the effect was compared with that of transforming growth factor (TGF)-beta. The daily periosteal injection of activin A increased the thickness of both the periosteal and bone matrix layers in a dose- and time-dependent manner. A maximal effect was obtained with 5.0 micrograms/day activin A. The time course of the effect of activin A on the periosteal thickness was similar to that of TGF-beta 1. However, the effect of TGF-beta 1 was much more pronounced and was mainly on fibroblasts and inflammatory cells. The time course of the effect of activin A on the thickness of bone matrix layer was different from that of TGF-beta 1. The effect of TGF-beta 1 reached maximum (1.8-fold) within 3 days, whereas that of activin A did not develop until day 6 and reached maximum at the end of the 12-day injection period (1.4-fold). Histological examinations revealed that both TGF-beta 1 and activin A increased the number of alkaline phosphatase-positive osteoblastic cells. These results demonstrate that periosteal injection of activin A stimulates bone formation. In addition, although the possibility cannot be ruled out that the dramatic effect of TGF-beta 1 on the periosteal layer might have affected the delivery of TGF-beta 1 to the bone surface, these observations also suggest that the mode of action of activin A may be different from that of TGF-beta 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Mesenchymal cell-based repair of large, full-thickness defects of articular cartilage

Osteochondral progenitor cells were used to repair large, full-thickness defects of the articular cartilage that had been created in the knees of rabbits. Adherent cells from bone marrow, or cells from the periosteum that had been liberated from connective tissue by collagenase digestion, were grown in culture, dispersed in a type-I collagen gel, and transplanted into a large (three-by-six-millimeter), full-thickness (three-millimeter) defect in the weight-bearing surface of the medial femoral condyle. The contralateral knee served as a control: either the defect in that knee was left empty or a cell-free collagen gel was implanted. The periosteal and the bone-marrow-derived cells showed similar patterns of differentiation into articular cartilage and subchondral bone. Specimens of reparative tissue were analyzed with use of a semiquantitative histological grading system and by mechanical testing with employment of a porous indenter to measure the compliance of the tissue at intervals until twenty-four weeks after the operation. There was no apparent difference between the results obtained with the cells from the bone marrow and those from the periosteum. As early as two weeks after transplantation, the autologous osteochondral progenitor cells had uniformly differentiated into chondrocytes throughout the defects. This repair cartilage was subsequently replaced with bone in a proximal-to-distal direction, until, at twenty-four weeks after transplantation, the subchondral bone was completely repaired, without loss of overlying articular cartilage. The mechanical testing data were a useful index of the quality of the long-term repair. Twenty-four weeks after transplantation, the reparative tissue of both the bone-marrow and the periosteal cells was stiffer and less compliant than the tissue derived from the empty defects but less stiff and more compliant than normal cartilage.

CLINICAL RELEVANCE

The current modalities for the repair of defects of the articular cartilage have many disadvantages. The transplantation of progenitor cells that will form cartilage and bone offers a possible alternative to these methods. As demonstrated in this report, autologous, bone-marrow-derived, osteochondral progenitor cells can be isolated and grown in vitro without the loss of their capacity to differentiate into cartilage or bone. Sufficient autologous cells can be generated to initiate the repair of articular cartilage and the reformation of subchondral bone. The repair tissues appear to undergo the same developmental transitions that originally led to the formation of articular tissue in the embryo.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of TGF-beta during in vitro differentiation of hamster tracheal epithelial cells

The control of growth and differentiation of tracheal epithelial cells is poorly understood. Retinoic acid seems to be essential for the growth and secretory cell differentiation of hamster tracheal epithelial (HTE) cells in culture. In this study, we tested the hypothesis that one way by which retinoic acid (RA) stimulates growth is by decreasing transforming growth factor beta (TGF beta) expression or activity or both. HTE cells were very sensitive to TGF beta-induced growth inhibition. TGF beta 1 was more potent than TGF beta 2 with 50% inhibition of growth achieved at a concentration less than 0.1 ng/ml. A single TGF beta 1 transcript of 2.4 kb was expressed in HTE cells, and the amount increased by fourfold as cell proliferation decreased and differentiation increased. No TGF beta 2 mRNA could be detected in proliferating undifferentiated HTE cells, but two distinct mRNAs (5.1 and 3.5 kb) were observed to be induced in a transient fashion in RA-treated cells which correlated with the onset of differentiation. The amount of biologically active TGF beta in conditioned media from HTE cells at different stages of growth and differentiation in primary culture was determined by the mink lung epithelial cell growth inhibition assay and the use of neutralizing antibodies. These assays indicated a large increase in the total amount of TGF beta at the time the cells slowed their growth and started to differentiate. The activity was due primarily to TGF beta 1. Interestingly, cells treated with RA had a major component of "preactivated" (non-latent) TGF beta 1 compared to control cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth factor responsiveness of human articular chondrocytes: distinct profiles in primary chondrocytes, subcultured chondrocytes, and fibroblasts

The objectives of this study were to establish a growth factor response profile for adult human articular chondrocytes, to determine whether this is unique for chondrocytes or influenced by the differentiation status of the cells, and to characterize growth factor interactions. It is shown that transforming growth factor-beta (TGF-beta) is the most potent mitogen among a variety of factors tested. All three isoforms of TGF-beta caused similar dose-dependent increases in chondrocyte proliferation. Other members of the TGF-beta family, including bone morphogenetic protein 2B (BMP2B), activin, and inhibin, did not detectably increase chondrocyte proliferation. Platelet-derived growth factor-AA (PDGF-AA), basic fibroblast growth factor (bFGF), and insulin-like growth factor 1 (IGF-1) also stimulated proliferation but were less effective than TGF-beta. In contrast to findings with other cell types, the effects of TGF-beta on chondrocyte proliferation were not dependent on the endogenous production of PDGF. The cytokines Interleukin 1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) gave no stimulation, but IL-1 inhibited chondrocyte proliferation induced by TGF-beta or serum. This response profile was characteristic for primary chondrocytes from human adults and distinct from subcultured (dedifferentiated) chondrocytes or skin fibroblasts. The latter preferentially responded to PDGF, and IL-1 caused greater increases in proliferation than TGF-beta. In summary, these results describe growth factor responses that are characteristic for chondrocytes and provide a basis for the analysis of changes in chondrocyte growth proliferation that occur in aging and tissue injury.

Evolution of the transforming growth factor-beta superfamily

Transforming growth factor beta 1 (TGF-beta 1) is the prototype of an increasingly complex superfamily of growth and differentiation factors. To date, a total of 74 TGF-beta-like sequences have been published, probably representing 23 distinct genes. These sequences were obtained from mammalian, avian, amphibian and insect species, thus emphasising the ancient nature of the TGF-beta superfamily peptides. This article summarises current hypotheses concerning the evolutionary history of this protein superfamily, based on the molecular phylogeny of the published sequences. Comparison of the deduced amino acid sequences leads to the definition of five main groups within the superfamily (TGF-beta, Bone Morphogenetic Proteins [BMP], Anti-Müllerian Hormone [AMH], Inhibin alpha [INH alpha] and GDF-9) and six subgroups within the BMPs (60A, Decapentaplegic [dpp], Vg1, BMP-3, Inhibin beta [INH beta A/B] and nodal). This classification predicts possible phylogenetic and functional relationships among these proteins.

Transforming growth factor beta increases ecto-nucleoside triphosphate pyrophosphatase activity of human bone-derived cells

Inorganic pyrophosphate (PPi) may be involved in the regulation of mineralization. The cell surface enzyme, ecto-NTP pyrophosphatase, could be a major source of extracellular PPi in bone, and agents that influence its activity in osteoblasts may modulate bone mineralization. We studied the effects of serum on the ecto-NTP pyrophosphatase activity of cultured human osteoblast-like cells. Enzyme activity was lowered when the concentration of fetal calf serum (FCS) was reduced from 10 to 2.5% (vol/vol) for 48 h, and a further decrease in activity was observed after 96 h. Relative to enzyme activity in cells cultured in serum-free medium for 96 h, adult human platelet-poor plasma (HPPP; 2.5-10% vol/vol) induced a small increase, similar concentrations of adult human serum (HS) induced much larger increases, and charcoal-depleted FCS was ineffective. In an attempt to identify the factor(s) present in serum that influence ecto-NTP pyrophosphatase activity, we examined transforming growth factor-beta (TGF-beta) and platelet-derived growth factor (PDGF). PDGFs AA, AB, and BB (0.1-10 ng/ml) were ineffective, but both TGF-beta 1 and TGF-beta 2 increased enzyme activity. The increase was dose dependent between 0.001 and 10 ng/ml, was enhanced in the presence of 2% vol/vol FCS, and was not potentiated by PDGF or by 1,25-(OH)2D3. Furthermore, the increase was independent of cell density and was blocked by inhibitors of protein and RNA synthesis. Ecto-NTP pyrophosphatase of subject-matched human dermal fibroblasts was unaffected by TGF-beta (10 ng/ml), suggesting that modulation of activity by the growth factor may be tissue specific. Alkaline phosphatase (ALP) probably serves to hydrolyze extracellular PPi in bone. In contrast to effects on NTP pyrophosphatase activity is osteoblast-like cells, TGF-beta 1 and TGF-beta 2 (0.001-10 ng/ml) decreased ALP activity dose dependently after 72 h. By inducing opposing changes in ecto-NTP pyrophosphatase and ALP activities, TGF-beta may increase extracellular PPi concentrations in osseous tissues and consequently modulate bone mineral properties in vivo.

Plasminogen-dependent activation of latent transforming growth factor beta (TGF beta) by growing cultures of osteoblast-like cells

Osteoblasts secrete transforming growth factor beta (TGF beta) as a biologically inert, latent complex that must be dissociated before the growth factor can exert its effects. We have examined the production and proteolytic activation of latent TGF beta (LTGF beta) by clonal UMR 106-01 rat osteosarcoma cells and neonatal mouse calvarial (MC) osteoblast-like cells in vitro. Synthetic bPTH-(1-34) increased the activity of tissue-type (tPA) and urokinase-type (uPA) plasminogen activators (PA) in cell lysates (CL) of UMR 106-01 cells. The concentration of active TGF beta in serum-free CM from cultures treated with bPTH-(1-34) and plasminogen was significantly greater than in CM from untreated controls and cultures treated with either bPTH-(1-34) or plasminogen alone. This effect occurred at concentrations of PTH-(1-34) that increased PA activity and was prevented by aprotinin, an inhibitor of plasmin activity. Treatment with bPTH-(1-34) had no effect on the concentration of TGF beta in acid-activated samples of CM. Functional consequences of proteolytically activated TGF beta was examined in primary cultures of neonatal MC osteoblast-like cells. Human platelet TGF beta 1 caused a dose-dependent increase in the migration of these cells in an in vitro wound healing assay. Cell migration was also stimulated in cultures treated with bPTH-(1-34) and plasminogen together. This effect was blocked by an anti-TGF beta 1 antibody. The results of these studies demonstrate that (1) LTGF beta secreted by osteoblasts in vitro is activated under conditions where the plasmin activity in the cultures is increased, and (2) the TGF beta generated by plasmin-mediated proteolysis is biologically active. We suggest that the local concentration of TGF beta in bone may be controlled by the osteoblast-associated plasminogen activator/plasmin system. Furthermore, since several calciotropic factors influence osteoblast PA activity, this system may have an important role in mediating their anabolic and/or catabolic effects.

Stimulatory effect of TGF-beta on anionic glycoconjugate synthesis by rat calvarial cells: specificity, uncoupling of cell density dependence, and modulation by chondroitin sulfate

Anchorage-dependent cultures of a population of cells derived from the outer part of the rat calvaria demonstrated decreased net accumulation of radiolabeled chondroitin sulfate (CS) and hyaluronic acid (HA) per cell as the cell density of the cultures increased. The addition of TGF-beta 1 resulted in large stimulations of the net CS, but not of the net HA, accumulating in the medium at all cell densities and an abolition of the density-dependent effect. These effects were largely due to increases in newly synthesized CS appearing in the medium. Supplementation of the culture media with CS had complex but relatively small effects on the stimulation of the net accumulation of radiolabeled medium CS by TGF-beta 1. The addition of TGF-beta 1 also resulted in a biphasic effect on cell growth that depended on the plating density, but cell growth differences could not account for the marked stimulation of CS synthesis by TGF-beta 1. Experiments with cycloheximide and beta-xyloside and isolation of the intact anionic glycoconjugates (AG) indicated that although synthesis of core protein was the limiting factor in CS synthesis, TGF-beta 1 stimulated the synthesis of CS chain when sufficient beta-xyloside acceptor was available. The overall results suggest that, in this cell system, the action of TGF-beta 1 on the synthesis of the major extracellular AGs is characterized by a relatively specific upregulation of CS proteoglycan (PG) synthesis and an uncoupling of the inhibitory effect of high cell density on CS PG synthesis.

Studies on growth plate chondrocytes in situ: cell proliferation and differentiation

In man, attaining full longitudinal growth and skeletal maturity may go towards preventing later problems, such as osteoporosis. In farmed species, it is becoming increasingly apparent that muscle growth or the calcium demands for reproduction have outstripped the ability of the skeleton to provide both support and sufficient calcium. Thus, understanding the mechanisms that control longitudinal growth is of vital importance. Methods for studying chondrocyte proliferation and differentiation increasingly rely on the use of isolated cells, but these do not reproduce in vivo conditions. It is therefore necessary to be able to assess chondrocyte function in situ in order to understand fully the actions of possible growth promoters and therapeutic agents. The control of chondrocyte proliferation seems to be heavily dependent on GH, which probably acts directly on the resting and proliferating chondrocytes (Fig. 3). In the former, it seems to regulate the commitment of prechondrocytes to the proliferative state, but the mechanisms whereby it achieves this are unclear. What is also unclear is the proportion of growth that is GH dependent and how much, if at all, the control of IGF-I production by nutritional and other factors contributes to longitudinal growth. The in situ biochemical approach has provided strong evidence that both TGF-beta and the c-myc proto-oncogene are involved in chondrocyte differentiation and may be early markers of this process (Fig. 3). Indirect evidence exists to support a role for c-myc expression in chondrocyte differentiation, as TGF-beta has been reported to have its mechanisms of action modulated by c-myc expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Molybdenum-induced changes in the epiphyseal growth plate

Molybdenum (Mo), at high concentrations, induces changes in the epiphyseal growth plate through its effects on copper (Cu) metabolism but it is unclear whether or not Mo can induce changes independent of its effects on copper status. To this end, the effect of Mo on longitudinal bone growth was examined in rats. Dietary Mo was given either as ammonium heptamolybdate or as ammonium tetrathiomolybdate, the latter producing a marked Cu deficiency. There was a significant reduction in longitudinal bone growth in both groups; however, growth plate width was increased only in the Cu-deficient animals due to an increase in the width of the zone of transitional/hypertrophic chondrocytes. Both glucose 6-phosphate dehydrogenase activity and cell proliferation (assessed by bromodeoxyuridine incorporation) were markedly decreased in the proliferating zone of the growth plate in both Mo-treated groups. These changes were not apparently related to changes in circulating vitamin D metabolites or insulin-like growth factor-1. The results indicate that excess Mo impairs cell proliferation within the growth plate, whereas the effects of copper deficiency are more related to chondrocyte differentiation. Thus, Mo can induce changes in longitudinal bone growth which are distinct from those resulting from Cu deficiency.

Osteoinductive proteins

Cartilage and bone tissues are rich in different polypeptide factors (growth factors) which participate in the regulation of skeletal development and growth. Parallels between the embryonal endochondral ossification, callus formation during fracture repair, and ectopic bone induction in postnatal life have encouraged scientists to search for common mechanisms underlying these processes. A set of polypeptide factors belonging to the TGF-beta superfamily called the bone morphogenetic proteins (BMPs), have been found to be of fundamental importance both in bone formation and mesenchymal-epithelial interactions in early embryogenesis. Thus, this group of proteins is a common denominator in all the above-mentioned processes involving osteoinduction and there is great potential for their clinical application as bone-inducing factors.

Transforming growth factor beta 1-induced cellular heterogeneity in the periosteum of rat parietal bones

We examined the osteogenesis process in transforming growth factor beta 1 (TGF-beta 1)-treated neonatal and adult rats, aiming to investigate the age difference in the effect of TGF-beta 1 on mesenchymal cell differentiation. Recombinant human (rh) TGF-beta 1 (20 and 200 ng) was injected onto the outer periostea of the right side of the parietal bone of each rat once a day for 1-12 days starting at the age of either 1 day or 12 weeks. On the day after the final injection, the calvaria was excised and evaluated histologically. In the neonates, the 12-day treatment with rhTGF-beta 1 increased the number of osteoprogenitor cells, resulting in intramembranous ossification. In the adult rats, rhTGF-beta 1 induced differentiation of chondrocytes. Cartilage masses were surrounded by mesenchymal cells, which would differentiate into chondrocytes. The cartilage matrix was partially calcified, with chondrocytes buried therein. In the calcified matrix, marrow cavities containing some multinuclear osteoclasts were formed. These findings indicate that rhTGF-beta 1 stimulated the differentiation of mesenchymal cells into chondrocytes and produced the cartilaginous matrix. rhTGF-beta 1 induced intramembranous ossification of the parietal bone in neonatal rats, and it induced enchondral ossification in adults. This result suggests that the different responses of mesenchymal cells in the periosteum to rhTGF-beta 1 may depend on the age of the animals used: namely, they may reflect the respective osteogenic stages of modeling and remodeling.

The secretion of transforming growth factor-beta by bovine luteal cells in vitro

Transforming growth factor-beta (TGF-beta), a multifunctional polypeptide growth factor, is produced by follicular cells in the ovary. However, there is little information indicating that TGF-beta is produced in the post-ovulatory follicle, i.e. the corpus luteum. In the present communication we present evidence that bovine luteal cells secrete large amounts of TGF-beta when maintained in moderate-term monolayer culture. Using TGF-beta 1 and TGF-beta 2 subtype-specific antibodies to neutralize the bioactivity it was found that 80-90% TGF-beta activity in luteal cell conditioned medium (LCCM) is due to TGF-beta 1, whereas < or = 10% TGF-beta activity in LCCM is due to TGF-beta 2. TGF-beta subtype nonspecific antibodies effectively and completely neutralized all TGF-beta activity in LCCM. The ratio of TGF-beta 1:TGF-beta 2 as estimated on the basis of neutralization studies was supported by visual observation of TGF-beta 1 and TGF-beta 2 protein bands on Western blotting. Using a modified and rapid mink lung epithelial cell bioassay and authentic TGF-beta to generate standard curves, the amount of TGF-beta secreted by luteal cells in vitro was quantitated. The concentration of luteal cell secreted proteins in the medium increased with time during 7 days of culture. Likewise, the TGF-beta concentration in LCCM increased during 7 days. To study the effect of duration of culture on the rate of TGF-beta secretion by luteal cells, conditioned medium was collected at 24 h intervals and replaced with fresh nutrient medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of expression of the chondrocytic phenotype in a skeletal cell line (CFK2) in vitro

We have examined in vitro the spontaneous and regulated expression of phenotypic characteristics associated with differentiated chondrocytes in an established skeletal cell line (CFK2) derived from fetal rat calvariae. Extended culture of CFK2 cells resulted in the appearance of glycosaminoglycans and type II collagen in the cell layer in association with the formation of focal nodes of cells. In addition, induction of mRNA-encoding link protein, cartilage-specific proteoglycan core protein, and thrombospondin was observed in the differentiated population (dCFK2 cells). The expression of these mRNAs was present for at least two passages after subculturing the dCFK2 cells. The dCFK2 cells also demonstrated enhanced parathyroid hormone (PTH)-stimulated adenylate cyclase activity. Proliferation of CFK2 cells was stimulated by the peptide regulatory factors EGF and PTH and inhibited by the steroidal agents dexamethasone and retinoic acid. EGF and retinoic acid inhibited the formation of cell foci and glycosaminoglycan deposition and the expression of mRNA-encoding link protein. In contrast, PTH and dexamethasone enhanced the formation of focal cellular nodes and augmented matrix deposition and link protein mRNA expression. These studies therefore show that the CFK2 cell line can serve as a nontransformed model of rat chondrocytic cells in which both induction and regulation of the expression of cartilaginous matrix components can be observed. This line thereby provides a unique renewable source of chondrocytic precursor cells and an excellent in vitro model for evaluating temporal and environmental control of chondrocyte differentiation and cartilage matrix production.

Recombinant human transforming growth factor beta 1 modulates bone remodeling in a mineralizing bone organ culture

TGF-beta 1 increases cell proliferation and collagen synthesis in osteoblast-like cells and bone organ cultures. However, the effects of TGF-beta 1 on bone resorption remain contradictory. Therefore, the exact role that this growth factor plays in the process of bone remodeling is still not clear. We studied the effects of recombinant human TGF-beta 1 (rhTGF-beta 1) on bone formation and resorption in a mineralizing bone organ culture system. Parietal bones from 20-day-old fetal rat calvariae were cultured up to 7 days in serum-free BGJb medium. They responded to a 1 day pulse or continuous treatment of rhTGF-beta 1 with dose-dependent increases in dry weight, [3H]thymidine ([3H]TdR) incorporation, and collagen synthesis. In contrast, rhTGF-beta 1 reduced the calcium content of the bones. This is not due to increased bone resorption but rather to failure of calcium deposition. The following responses occurred at 1 nM rhTGF-beta 1. Dry weight was increased 25-50% after 6 days in culture. DNA synthesis was increased to a maximum at day 1, reaching twofold of the control level. Adding hydroxyurea at day 0 reduced [3H]TdR incorporation in rhTGF-beta 1 treated bones to 20% of the control and indomethacin abrogated the increase in [3H]TdR stimulated by rhTGF-beta 1 to the control level. Both treatments completely blocked the increase in dry weight induced by rhTGF-beta 1 at day 6. rhTGF-beta 1 stimulated collagen synthesis to reach its maximum at day 2, with a twofold increase in [3H]proline incorporation. Basal alkaline phosphatase activity fell continuously in culture, reaching 35% of day 0 level at day 6. Enzyme activity was not altered by rhTGF-beta 1. Morphologic observations by light and electron microscopy confirmed these findings. In summary, rhTGF-beta 1 altered bone remodeling by increasing organic components and decreasing calcification in a mineralizing bone organ culture system.

Micronutrients and longitudinal growth

The present review has concentrated on the control of longitudinal growth and the relative importance of certain micronutrients. By far the most significant of these is 1.25(OH)2D3 which is now being recognized, not only for its role in maintaining Ca homeostasis, but also its major role in chondrocyte differentiation within the growth plate.

1,25-Dihydroxy vitamin D3 stimulation of TGF-beta expression in chick embryonic calvarial bone

Bone is a highly active producer of the cytokine, transforming growth factor-beta (TGF-beta), which is likely to be functionally involved in the regulation and maintenance of bone development and growth. In addition, bone functions are also regulated by the major calciotropic hormone, 1,25-dihydroxy vitamin D3 (1,25(OH)2D3). This investigation aims to examine the possible relationship between TGF-beta and 1,25(OH)2D3 using an unique calcium-deficient chick embryonic model. By means of long-term culture without the eggshell (shell-less or SL culture), chick embryos may be rendered severely calcium-deficient with gross undermineralization of the skeleton. We have previously observed that the calvaria of these SL embryos develop abnormal chondrogenic phenotype, with production of collagen type II, and elevated TGF-beta expression. Administration of 1,25(OH)2D3 to the SL embryos in vivo on incubation days 10 and 12 (SL + D embryos) resulted in near-normal serum calcium on day 14 and improved calvarial calcification. However, TGF-beta expression in the SL + D calvaria was further increased compared to untreated SL calvaria, when analyzed at both the mRNA and protein levels. Histolocalization of gene expression by immunohistochemistry and in situ hybridization revealed that cells in the less mineralized orbital and temporal zones of the calvarium are particularly affected by the 1,25(OH)2D3 treatment. Interestingly, the increased TGF-beta expression resulting from 1,25(OH)2D3 treatment did not correct the aberrant collagen phenotype in the SL calvaria. These observations suggest that TGF-beta expression by bone cells in situ is stimulated by 1,25(OH)2D3, and that normal cellular differentiation and morphogenesis of the embryonic calvaria are dependent on proper and balanced TGF-beta expression as well as the state of tissue mineralization.

Effects of hyperthermia on bone. II. Heating of bone in vivo and stimulation of bone growth

Previous studies in vitro have shown that it is possible to achieve comparable temperature distribution in bone and the adjacent soft tissues, under appropriate experimental conditions. The objective of the present work was to determine the effects of hyperthermia on bone in vivo. In order to obtain direct temperature measurements in bone, catheters were surgically installed on top of and inside the medullary cavity of the femur of normal rabbits. The thighs were irradiated with 915 MHz microwaves for 45 min, once or twice a week. The temperatures on and inside the bone were maintained between 42.5 and 44.0 degrees C; the resulting temperatures in the muscle were within 1.0 degrees C at depths equidistant from the applicator. After four to six treatments the femora were excised for histopathological examination. New trabecular bone was deposited around the catheters; most bone components including periosteum, osteoid, and fully calcified matrix could be seen. Large numbers of osteoblasts and osteoclasts lined the trabecular surfaces, and numerous cement lines were visible, running in all directions, indicating extensive bone deposition and remodelling. In contrast, control bones (catheters installed--no hyperthermia) showed much less ossification, with many areas of thin incomplete osteoid. Further, bones treated with hyperthermia only (no surgical trauma) showed no such changes. Thus, it appears that following an initial insult, hyperthermia promotes bone deposition.

Role of transforming growth factor-beta in chronic lymphocytic leukemia

TGF-beta is an important immunoregulator as it suppresses proliferation and function of B- and T-lymphocytes. In the present study we have examined the cellular localization and secretion of TGF-beta in B-cells from normal donors and patients with CLL and have assessed the influence of TGF-beta 1 on DNA synthesis in these cells. Using anti-LC(1-30)--a polyclonal anti-TGF-beta 1 antibody--TGF-beta was localized to discrete sites within the cytoplasm of both normal and malignant lymphocytes. These areas co-localized with areas detected by an antigranule antibody (D545), suggesting that TGF-beta may be stored within cytoplasmic secretory vesicles. Both normal B- and CLL cells contained low or undetectable levels of TGF-beta mRNA and secreted low and equivalent amounts of TGF-beta. Compared to untreated cells, DNA synthesis was reduced by TGF-beta 1 to a mean +/- S. E. of 0.84 +/- 0.07 in CLL cells and this was significantly less (p < 0.001) than that observed in normal B-cells (mean +/- S. E. of control, 0.12 +/- 0.02). In 3 of the 18 patients, TGF-beta 1 stimulated DNA synthesis. The reduced inhibition of leukemic cell DNA synthesis by TGF-beta 1 in CLL may provide these cells with a growth or survival advantage over normal lymphocytes and contribute to their selective accumulation.

Transforming growth factor beta exerts opposite effects from interleukin-1 beta on cultured rabbit articular chondrocytes through reduction of interleukin-1 receptor expression

OBJECTIVE

The aim of the study was to determine whether transforming growth factor beta (TGF beta) modulates the effects and the receptor expression of interleukin-1 (IL-1) in rabbit articular chondrocytes (RAC).

METHODS

Collagen, glycosaminoglycan, and collagenase production, together with 125I-labeled IL-1 binding, were analyzed in RAC cultures.

RESULTS

TGF beta reduced both IL-1 effects on matrix metabolism and IL-1 receptor expression.

CONCLUSION

TGF beta acts as an antagonist of the effects of IL-1 through down-regulation of its receptor expression.

The effect of transforming growth factor beta on the plasminogen activator activity of normal human osteoblast-like cells and a human osteosarcoma cell line MG-63

Transforming growth beta (TGF-beta) has been proposed to have a role in bone remodeling by affecting the differentiation and activity of osteoblasts and osteoclasts and by inhibiting the production of proteinases, such as plasminogen activators (PAs). Studies on PAs have largely been based on data from nonhuman and fetal cell lines, however. The purpose of this study was to investigate the effect of TGF-beta on the PA activity of normal human osteoblast-like cells and to compare this with its action on the human osteosarcoma cell line MG-63. The action of interleukin-1 beta (IL-1 beta) was also assessed because it has been shown to increase PA activity in other connective tissue cell types. Normal osteoblast-like cells had low to undetectable basal urokinase (uPA) and tissue plasminogen activator (tPA) activity, which was significantly stimulated by TGF-beta 1. This action was shown to be dependent on transcription and new protein synthesis. TGF-beta 2 had a similar action. IL-1 beta did not stimulate PA activity. In contrast, the MG-63 cell line had high basal tPA and uPA activities. TGF-beta 1 decreased basal PA activity, the effect being most marked for uPA activity. IL-1 beta stimulated uPA and tPA activity. TGF-beta 1 inhibited IL-1 beta-stimulated uPA activity, but the effect on tPA was more variable. This study has shown that TGF-beta has opposite effects on the PA activity of the two osteoblast-like cell types studied. Care must therefore be used before extrapolating data from one cell type to another.(ABSTRACT TRUNCATED AT 250 WORDS)

Initiation of bone regeneration in adult baboons by osteogenin, a bone morphogenetic protein

Osteogenin, and related bone morphogenetic proteins, induce endochondral bone differentiation through a cascade of events which include formation of cartilage, hypertrophy and calcification of the cartilage, vascular invasion, differentiation of osteoblasts, and formation of bone. These events have been studied in a postnatal model of bone development in rodents. Information concerning the morphogenetic potential of osteogenin in primates is a prerequisite for potential clinical application in man. The efficacy of allogeneic osteogenin in primates was investigated in both extraskeletal and skeletal sites in 19-Chacma baboons (Papio ursinus). Osteogenin was isolated from demineralized baboon bone matrix and purified by chromatography on heparin-Sepharose, hydroxyapatite, and Sephacryl S-200. Protein fractions with a molecular mass range of 26-42 kDa induced cartilage and bone differentiation in the subcutaneous space of rats. Final purification to homogeneity was obtained by electroendosmotic elution from a preparative sodium dodecyl sulphate (SDS) polyacrylamide gel, resulting in a single band on a SDS-polyacrylamide gel with an apparent molecular mass of 30-34 kDa, with biological activity in rats. The osteoinductive potential of osteogenin in primates was tested first in intramuscular sites in baboons and found to be active. The bone regeneration potential was investigated in nonhealing calvarial defects surgically prepared in adult male baboons. Baboon osteogenin induced complete regeneration of the cranial wound. These findings in adult primates establish a primary role for osteogenin in initiation and promotion of osteogenesis, and imply a potential therapeutic application based on cell biology of extracellular matrix-cell interactions.

Transforming growth factor beta 1 is an epithelial-derived signal peptide that influences otic capsule formation

Interactions between epithelial and mesenchymal tissues in the developing inner ear direct the formation of its cartilaginous capsule. Recent work indicates that many growth factors are distributed in the early embryo in vivo in a temporal-spatial pattern that correlates with sites of ongoing morphogenetic events. We report here that the localization of transforming growth factor beta 1 (TGF-beta 1) in both epithelial and mesenchymal tissues of the mouse inner ear between 10 and 16 days of embryonic development (E10-E16). In addition, utilizing a high-density culture system as an in vitro model of otic capsule chondrogenesis, we show that modulation of chondrogenesis by TGF-beta 1 in cultured mouse periotic mesenchyme mimics the in vitro effects of otic epithelium on the expression of chondrogenic potential. We provide evidence of a causal relationship of this growth factor to otic capsule formation in situ by demonstrating that the actual sequence of chondrogenic events that occur in the developing embryo is reproduced in culture by the addition of exogenous TGF-beta 1 peptide. Furthermore, in cultures of mesenchyme containing otic epithelium, we demonstrate the localization of endogenous TGF-beta 1, first within the epithelial tissue and later within both the epithelium and its surrounding periotic mesenchyme, contrasted to an absence of endogenous TGF-beta 1 in cultures of mesenchyme alone. Our results suggest that TGF-beta 1 is one of the signal molecules that mediate the effects of otic epithelium in influencing the formation of the cartilaginous otic capsule.

cDNA cloning and sequence analysis of beta ig-h3, a novel gene induced in a human adenocarcinoma cell line after treatment with transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) is capable of affecting the proliferation of many cell types. To identify novel genes whose protein products may mediate cellular responses to this factor, a cDNA library was made from mRNA isolated from a human lung adenocarcinoma cell line (A549) that had been treated for 3 days with TGF-beta. The library was screened by differential hybridization and a cDNA clone, beta ig-h3, was isolated. This gene was induced up to 20-fold in A549 cells after 2 days of treatment with TGF-beta 1. It was also induced in several other cell lines, including PC-3 and H2981. DNA sequence analysis of beta ig-h3 indicated that it encoded a novel protein, beta IG-H3, of 683 amino acids, which contained an amino-terminal secretory sequence and a carboxy-terminal Arg-Gly-Asp (RGD) sequence that can serve as a ligand recognition site for several integrins. beta IG-H3 also contained short amino acid regions homologous to similar regions in Drosophila fasciclin-I and four homologous internal domains, which can be folded into a potential bivalent structure and could act as a bridge between cells expressing the appropriate ligand. beta ig-h3 RNA was detected in several cell lines and tissues. COS cells transfected with plasmids encoding beta IG-H3 secreted a major 68-kD protein that was detected by immunoblotting using antipeptide antibodies. Since beta ig-h3 is induced in several cell lines whose proliferation is affected by TGF-beta 1, it may be involved in mediating some of the signals of this multifunctional growth modulator.

Cloning and developmental expression of Sna, a murine homologue of the Drosophila snail gene

The genetic analysis of dorsoventral patterning in Drosophila has identified a zinc-finger gene, snail, that is required for mesoderm formation. The cloning and nuclease protection analysis of a Xenopus homologue of this gene has suggested a possible role in the mesoderm of vertebrates. Here, we describe the cloning of a murine homologue of snail, Sna, and in situ hybridisation studies of its developmental expression. Sequence analysis reveals substantial conservation of the second to fifth zinc fingers, but not of the first zinc finger in the Sna gene. Expression occurs in the ectoplacental cone, parietal endoderm, embryonic and extraembryonic mesoderm, in neural crest and in condensing precartilage. Based on the timing and spatial restriction of expression in embryonic mesoderm, we suggest that Sna might be required for the early development of this tissue, as is the case for its Drosophila counterpart. In addition, we propose that Sna might have an analogous role in the development of neural crest. The expression in condensing precartilage indicates that this gene also has a later function in chondrogenesis.

Inhibin alpha- and beta A-subunit immunoreactivity in the chicken embryo during morphogenesis

Antibodies against synthetic peptides selected from the amino acid sequences of human inhibin alpha- and beta A-subunits were used to examine the distribution of inhibin subunit immunoreactivity in chicken embryos during the first week of development. Inhibin alpha-subunit immunoreactivity was localized in skeletal and smooth muscle myoblasts as well as developing cardiac muscle cells. In somites, immunostaining was seen exclusively in myotomes. The appearance of alpha-subunit immunoreactivity was correlated with myogenic differentiation; immunoreactivity was not seen in non-differentiated mesenchymal cells or in terminally differentiated adult muscle cells. In cardiac muscle, some immunopositive myocytes were seen also in the adult. In the adult heart, the Purkinje fibers were strongly immunoreactive, suggesting a possible role of the immunoreactive protein in the impulse-conducting function of these specialized cells. Inhibin alpha-subunit immunoreactivity was also seen in the visceral and parietal cells of the Bowman's capsule in both mesonephric and metanephric kidneys. In addition to mesodermal derivatives, alpha-subunit immunoreactivity was localized in neuroepithelial cells and axons in the developing central nervous system. Immunoblotting with anti-alpha(1–32) revealed two protein bands with M(r) values of 50,000 and 32,000 in cytosol samples of whole embryos under nonreducing conditions. In reduced samples an approximately 14,000 M(r) protein species was detected. Inhibin beta A-subunit immunoreactivity was detected only in chondrocytes, suggesting that the immunoreactive protein might represent a chicken homologue of the various cartilage and bone morphogenetic proteins expressed in mammals.

Transforming growth factor-beta 1 mRNA in neonatal ovine molars visualized by in situ hybridization: potential role for the stratum intermedium

Human dentine contains relatively large amounts of transforming growth factor-beta (TGF-beta), which might originate from odontoblasts. The expression of the TGF-beta 1 message in developing teeth was examined by in situ hybridization. The analysis was made on 5-microns serial sections of mandibular third molars of neonatal sheep cut from tissues that had been fixed in glutaraldehyde and paraffin-embedded. A 35S-labelled cRNA probe, complementary to TGF-beta 1 mRNA, was constructed from human TGF-beta 1 cDNA. Northern analysis of total RNA from sheep placenta and neonatal third molars demonstrated hybridization to a single 2.4 kb TGF-beta 1 transcript from both tissues, indicating cross-reactivity of the human probe in the sheep. In the neonatal molars, in situ hybridization was observed in cells of the inner enamel epithelium, mature ameloblasts and mature odontoblasts, but not within preodontoblasts before dentine matrix formation. TGF-beta 1 mRNA expression was also evident in the cells of the dental papilla but scarcely so in the stellate reticulum. The most striking feature was the appearance of hybridization signal in the cells of the stratum intermedium before hybridization was evident in the inner enamel epithelium. Control sections incubated with RNAase before incubation with probe did not show evidence of hybridization. These findings suggest that TGF-beta 1 may have an important regulatory role in the differentiation of ameloblasts and odontoblasts, perhaps by modulating matrix formation during amelogenesis or odontogenesis. They also suggest a potential novel regulatory role for the cells of the stratum intermedium.

Enhancement of osteoinduction by vitamin D metabolites in rachitic host rats

Diaphyseal bone from normal Sprague-Dawley rats was delipidated in chloroform-methanol and demineralized in 0.6 N HCl at 4 degrees C. The bones were then implanted for 7-28 days into rats made rachitic by a low-phosphate, vitamin D-deficient diet (VDP-) for 3 weeks. Bones from VDP- and normal rats were also implanted into normal hosts. When normal rats were used as the host environment, a consistent sequence of cartilage induction and bone formation was observed. Demineralized rachitic bone (RB) implanted into normal host rats resulted in cartilage and bone induction similar to that seen for normal bone (NB) implants. Transmission electron microscopy of RB in normal hosts revealed morphologically normal chondrocytes and cartilage matrix with normal mineralization. In contrast, implantation of NB in VDP- hosts resulted in delayed chondrogenesis and lack of calcification. Furthermore, similar results were observed when RB was implanted into VDP- hosts. Treatment of VDP- hosts with either 1 alpha-hydroxyvitamin D3 or 24,25-dihydroxyvitamin D3 did not accelerate the sequential appearance of precartilage or cartilage. However, 24,25-(OH)2D3 administered alone or in combination with 1 alpha-OHD3 significantly increased the amount of calcified cartilage observed at 2 weeks postimplantation compared to implants from either untreated VDP-hosts or those treated only with 1 alpha-OHD3. New bone formation was observed at 4 weeks postimplantation in all vitamin D-treated groups as determined by von Kossa staining or direct electron microscope examination. There was no apparent difference in the quantitative or qualitative bone formed within the various vitamin D-treated groups. Serum calcium and phosphorus levels were lower and alkaline phosphatase levels were higher in VDP- hosts compared with normal animals or those treated with vitamin D metabolites. The results of this study show a reduction in the capacity of progenitor cells in VDP- rat hosts to respond to osteoinductive factor(s). This impaired response appears to be corrected by vitamin D metabolites.

Crystal structure of transforming growth factor-beta 2: an unusual fold for the superfamily

The transforming growth factors-beta (TGF-beta 1 through -beta 5) are a family of homodimeric cytokines that regulate proliferation and function in many cell types. Family members have 66 to 80% sequence identity and nine strictly conserved cysteines. A crystal structure of a member of this family, TGF-beta 2, has been determined at 2.1 angstrom (A) resolution and refined to an R factor of 0.172. The monomer lacks a well-defined hydrophobic core and displays an unusual elongated nonglobular fold with dimensions of approximately 60 A by 20 A by 15 A. Eight cysteines form four intrachain disulfide bonds, which are clustered in a core region forming a network complementary to the network of hydrogen bonds. The dimer is stabilized by the ninth cysteine, which forms an interchain disulfide bond, and by two identical hydrophobic interfaces. Sequence profile analysis of other members of the TGF-beta superfamily, including the activins, inhibins, and several developmental factors, imply that they also adopt the TGF-beta fold.

Cell density dependent effects of TGF-beta demonstrated by a plasminogen activator-based assay for TGF-beta

Transforming growth factor-beta 1 (TGF-beta 1) induces a decrease in plasminogen activator (PA) expression in confluent cultures of bovine aortic endothelial (BAE) cells. We describe an assay using the suppression of PA expression in confluent BAE cells by TGF-beta 1 which detects concentrations of the growth factor ranging from 5 to 200 pg/ml and has an ED50 of 15-20 pg/ml. The assay can be performed in 96-well plates and requires a minimum of 35 ul of solution per sample, thereby limiting the amount of reagents required and allowing many samples to be tested in a single assay. Here we demonstrate that the effect of TGF-beta 1 on PA expression in BAE cells depends on the length of time the cells are exposed to the growth factor and the density at which the cells are plated. In cells plated at a high density (3.5 x 10(5) cells/cm2), both 4 h and 24 h exposures to TGF-beta 1 suppress PA expression. However, with cells plated sparsely (3.5 x 10(4) cells/cm2), a 4 h exposure to TGF-beta 1 increases PA expression 2-fold, whereas a 24 h exposure results in an 85% inhibition of basal PA expression. The paradoxical stimulation of PA expression in cells at a sparse density upon 4 h exposure to TGF-beta 1 occurs in a dose-dependent manner with an ED50 of 15-20 pg/ml. This bifunctional response of PA production in cells exposed to TGF-beta 1 may have implications with regard to the role of TGF-beta 1 in angiogenesis.

The proto-oncogene c-myc is involved in cell differentiation as well as cell proliferation: studies on growth plate chondrocytes in situ

A combination of immunocytochemistry and microdensitometry has been used to localize and quantify the expression of the proto-oncogene c-myc within chondrocytes of the proximal growth plates of rat and chick long bones. Although the c-myc protein was localized in all chondrocytes of the growth plate of both species the most intense staining was restricted to the proliferating and differentiating chondrocytes. These were identified by their ability to synthesize DNA (bromodeoxyuridine positive) and the presence of alkaline phosphatase activity, respectively. Species differences did exist with the c-myc concentration of the chick proliferating and differentiating chondrocytes being higher (128% and 240%, respectively) than the respective chondrocytes of the rat. The higher c-myc concentration in the chick proliferating chondrocytes paralleled the differences in the bromodeoxyuridine labelling index between the two species. In the rat, the concentration of c-myc protein present in the differentiating chondrocytes was 74% higher than in the respective proliferating chondrocytes, while in the chick it was 146% higher. The data not only provides further evidence for a role of the c-myc protein in cell proliferation but also suggests involvement of this protein in chondrocyte differentiation and/or hypertrophy.

Crystallization and preliminary X-ray analysis of recombinant human transforming growth factor beta 2

Recombinant human transforming growth factor beta 2 (TGF-beta 2) was cloned and expressed in E. coli. The protein was isolated from inclusion bodies, renatured and purified to a single component as judged by reversed-phase HPLC. The recombinant TGF-beta 2 was shown to have a biological activity equal to that of native TGF-beta 2 in a fibroblast migration assay. Pure, active recombinant TGF-beta 2 has been crystallized from polyethylene glycol 400. The trigonal crystals of spacegroup P3(1)21 or P3(2)21 have unit cell dimensions of a=b=60.6 A, c=75.2 A and diffract beyond 2.0 A.

Differential expression of TGF beta isoforms by human articular chondrocytes in response to growth factors

Transforming growth factor beta (TGF beta) is a family of important regulators of chondrocyte growth and differentiation. Although TGF beta has been detected in cartilage, the TGF beta isoforms expressed by chondrocytes and their regulation by growth factors are unknown. This study shows that human articular chondrocytes release TGF beta activity. Chondrocyte conditioned media contains active TGF beta and larger quantities in latent form. By neutralization with specific antibodies it is shown that all three isoforms (TGF beta 1, TGF beta 2, and TGF beta 3) are secreted by chondrocytes. Analysis of the inducers of TGF beta gene expression demonstrates complex regulation of TGF beta production by growth factors. Basic fibroblast growth factor (bFGF) stimulates the release of TGF beta activity but has no effect on steady state TGF beta mRNA levels while platelet-derived growth factor (PDGF) upregulates TGF beta 1 and TGF beta 3 mRNAs with a corresponding increase in protein secretion. The three TGF beta isoforms themselves differentially affect gene expression. While TGF beta 1 and TGF beta 2 show autoinduction, TGF beta 3 upregulates TGF beta 1 but does not affect TGF beta 2 mRNA levels. These results demonstrate that human articular chondrocytes produce all three TGF beta isoforms. Induction of TGF beta expression is differentially regulated by various growth factors and occurs at the mRNA level and/or posttranscriptionally. Chondrocyte expression and the differential regulation of TGF beta 1, TGF beta 2, and TGF beta 3 by growth factors suggest that all three isoforms of TGF beta are part of the network of cartilage regulatory factors.

Regulation of murine embryonic epithelial cell differentiation by transforming growth factors beta

The expression of some members of the transforming growth factor beta (TGF beta) family of genes in embryonic craniofacial tissue suggests a functional role for these molecules in orofacial development. In an attempt to ascertain a role for the TGF beta s during palatal ontogeny, murine palatal shelves were excised on gestation day (GD) 12, prior to overt epithelial differentiation, grown in organ culture under serum-free conditions and exposed to TGF beta 1 and TGF beta 2 for 18 or 42 h. Shelves were labeled with [3H]-thymidine (20 microCi/ml) during the last 4 h in culture, fixed, dehydrated, embedded in paraffin and sections stained and examined by autoradiography. Treatment of GD12 palates with TGF beta 1 and TGF beta 2 resulted in precocious cessation of medial edge epithelium (MEE) DNA synthesis followed by elimination of the MEE. In addition, this response appeared to be dose-related with higher concentrations of growth factor eliciting a more marked biological response. TGF beta treatment of homologous shelves grown in apposition also resulted in precocious fusion of apposing MEE. Thus, members of the TGF beta family, known to be synthesized by palatal MEE, appear to act in an autocrine/paracrine fashion in this tissue and are capable of regulating differentiation of embryonic palatal medial edge epithelium.

B-cell chronic lymphocytic leukaemia cells express and release transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) has been described as a potent inhibitor of various cell types, among others of primitive haematopoietic progenitors in vitro, and as a negative autocrine regulator of normal B lymphocyte growth and differentiation. In the present study we investigated TGF-beta gene expression in peripheral blood mononuclear cells (PBMC) and in B cells from patients with B-cell chronic lymphocytic leukaemia (B-CLL) and from normal controls. Monocyte depleted B-CLL cells expressed constitutively mRNA for TGF-beta 1 and secreted low amounts of TGF-beta activity into the culture medium. Stimulation of cells by phorbol ester noticeably enhanced mRNA levels as well as protein secretion in most cases. TGF-beta activity was of the same magnitude as in normal controls. We next analysed TGF-beta in highly enriched B lymphocytes from B-CLL (95-100% CD19+), and found that TGF-beta secretion was up to 3 times higher than in the original PBMC population. It is discussed that B-CLL cells might escape from negative regulation by TGF-beta and, on the other hand, inhibit normal haematopoietic cell proliferation and thereby achieve a growth advantage in the haematopoietic tissues.

Effect of systemic calcium deficiency on the expression of transforming growth factor-beta in chick embryonic calvaria

The developmental process of intramembranous ossification involves bone formation directly from mesenchymal differentiation without a cartilage intermediate. We have previously observed that systemic calcium deficiency in the developing chick embryo, produced by long-term shell-less culture, results in the appearance of chondrocyte-like cells in the calvarium, a parietal bone which normally develops via intramembranous ossification. This investigation aims to analyze the mechanism underlying this calcium deficiency-related, aberrant appearance of cartilage phenotype in the chick embryonic calvarium. In view of the reported involvement of transforming growth factor beta (TGF-beta) in osteogenesis and chondrogenesis, we have examined and compared here the expression of TGF-beta in the chick embryonic calvaria of normal (in ovo development, NL), shell-less (SL), and calcium-supplemented SL (SL+Ca) embryos. TGF-beta expression was analyzed at the mRNA level by blot and in situ cDNA hybridization, and at the protein level by immunohistochemistry and immunoblotting. The results presented here indicate that: 1) TGF-beta is expressed in the chick embryonic calvarium by both periosteal cells and osteocytes, as revealed by in situ hybridization and immunohistochemistry; 2) TGF-beta expression is significantly increased in SL calvarium compared to NL calvarium, at both protein and mRNA levels; 3) the number of TGF-beta expressing cells increases in the SL calvarium, particularly along the central, subcambial core region of the bone; and 4) exogenous calcium repletion to the SL embryo affects the expression of TGF-beta such that the pattern approaches that in the NL embryo. Taken together, these results indicate that altered TGF-beta expression accompanies the aberrant appearance of cartilage phenotype caused by systemic calcium deficiency. We postulate that normal cellular differentiation along the osteogenic pathway during embryonic intramembranous ossification is crucially dependent on regulated TGF-beta expression.

Growth and morphogenetic factors in bone induction: role of osteogenin and related bone morphogenetic proteins in craniofacial and periodontal bone repair

Bone has considerable potential for repair as illustrated by the phenomenon of fracture healing. Repair and regeneration of bone recapitulate the sequential stages of development. It is well known that demineralized bone matrix has the potential to induce new bone formation locally at a heterotopic site of implantation. The sequential development of bone is reminiscent of endochondral bone differentiation during bone development. The collagenous matrix-induced bone formation is a prototype model for matrix-cell interactions in vivo. The developmental cascade includes migration of progenitor cells by chemotaxis, attachment of cells through fibronectin, proliferation of mesenchymal cells, and differentiation of bone. The bone inductive protein, osteogenin, was isolated by heparin affinity chromatography. Osteogenin initiates new bone formation and is promoted by other growth factors. Recently, the genes for osteogenin and related bone morphogenetic proteins were cloned and expressed. Recombinant osteogenin is osteogenic in vivo. The future prospects for bone induction are bright, and this is an exciting frontier with applications in oral and orthopaedic surgery.

Regulation of amphiregulin mRNA by TGF-beta in the human lung adenocarcinoma cell line A549

Transforming growth factor beta is a strong growth inhibitor for many types of normal and transformed cells, although little is known on the mechanism of this anti-proliferative effect. The human lung adenocarcinoma cell line A549 is growth arrested by TGF-beta 1 and serves as a model for studying this effect. We describe that, concurrent with the inhibition of A549 cell growth, TGF-beta 1 treatment causes a dramatic reduction in the level of expression of the amphiregulin (AR) gene, a recently identified member of the EGF/TGF alpha family. Similar results were also observed with TGF-beta 2. Peak inhibition occurred at 24 hr of treatment and was reversible upon removal of TGF-beta 1. The level of AR protein secreted by A549 cells was also decreased by TGF-beta 1. In contrast, TGF-alpha mRNA was not detected in these cells regardless of TGF-beta 1 treatment. Another TGF-beta inhibited cell line, PC-3 (human prostatic adenocarcinoma) also exhibited a decrease in AR message levels following exposure to TGF-beta 1. The growth inhibitory effects of TGF-beta may in part be mediated by modulation of AR expression.